A member of the benzopyrone group of chemicals, coumarin is a sweet-scented compound, recognisable as the smell of newly-mown hay present in the ground-covering woodlander, Galium odoratum (sweet woodruff). Although Coumarin itself has no anti-coagulant properties, it can be transformed either synthetically or by some fungi into the anti-coagulant dicoumerol.
The drug Warfarin is synthesised from 4-hydroxycoumarin and is commonly used to treat heart attacks and as rat poison!
Coumarin has appetite suppressant properties, which, coupled with its bitter taste, reduces the impact of grazing animals in plants such as sweet clover and sweet woodruff, which contain large quantities. It is moderately toxic.
Galium odoratum, sweet woodruff, produces tiny white flowers in cymes above mid green lanceolate leaves arrange in stars around the stem in spring. The sweet hay scent strengthens when the foliage is dried and has been used to scent laundry and in pot pourri since medieval times.